FIG. 1 is a cross-sectional view of a prior-art cooling fan 3, as used in motor vehicles, which cools a radiator (not shown), which extracts heat from engine coolant. A motor 4 rotates a cylindrical hub 5, as indicated by arrow 6, which hub 5 carries fan blades 3. Arrows 7 indicate moving air streams.
One feature of such a fan is that it increases static pressure at point A1, compared with point A2. This pressure differential causes leakage air, indicated by arrows 8 and 8A, to flow in the space between the fan ring 9 and the shroud 12.
This leakage represents a loss in efficiency, since the leaked air was initially pumped or moved to the pressure at point A1, but then drops to the pressure at point A2, but with no work or other useful function being accomplished.
It may appear that the airflow indicated by arrow 8 is penetrating a solid body, namely, the strut 18 which supports stator 21. However, this appearance is an artifact of the cross-sectional representation of FIG. 1. In fact, spaces exist between adjacent stators 21, as indicated schematically by space 24 in FIG. 3. Air can flow as indicated by arrow 27, which corresponds in principle to arrow 8 in FIG. 1.
FIGS. 2A-2D are copies of the like-numbered Figs. in U.S. Pat. No. 5,489,186, and represent strategies proposed by that patent to (1) reduce the leakage and (2) accomplish other beneficial objects.